Which instrument is used to measure current in a circuit?

• A. Ammeter
• B. Voltmeter
• C. Wattmeter
• D. Ohmmeter

Answer: (A)

Current is the rate at which charge flows, so to measure it you need a device that the same current can pass through. An ammeter is designed for this purpose and is wired in series with the circuit so all the current flows through it. Because it has very low internal resistance, it minimizes any disturbance to the circuit while giving a reading in amperes of how much current is flowing.

Voltmeter measures voltage and is connected in parallel across a component, and it uses a high internal resistance to avoid drawing current. Ohmmeter measures resistance by applying a small voltage and observing the current, and is used when the circuit is off. Wattmeter measures power, which requires both current and voltage in its calculation, not just current alone. So the instrument used to measure current is the ammeter.